Bone fixation device

ABSTRACT

A bone fixation apparatus and associate method. The bone fixation apparatus includes a plate having a fixation hole, and a modular fastener received in the fixation hole. The bone fixation fastener includes a shaft member and an expandable head member. The shaft member has a outer cam at a first end mating with a corresponding inner cam of the head member, such that upon rotation of the head member relative to the shaft member, the head member expands against an inner surface of the fixation hole to prevent back out of the shaft member relative to the bone fixation plate.

INTRODUCTION

In certain orthopedic surgical procedures, it is necessary to securemultiple bones or bone portions relative to each other. For example, inspinal surgeries, the fusion of two or more vertebrae bodies is requiredto secure a portion of the spinal column in a desired position. Thisneed may be the result of physical trauma from fractures ordislocations, degenerative diseases, or tumors.

One such spinal fixation procedure involves the attachment of aprosthesis or plate to the anterior side of the cervical portion of thespine. The procedure requires anteriorly accessing the spine andsecuring a prosthetic plate to the one or more cervical vertebrae. Thisallows fusion of the one or more cervical vertebrae in a particularorientation so to facilitate healing or to repair a condition of thepatient.

Various fusion plates and plating systems are known for anteriorlyfusing the cervical spine. Such plates and plating systems must meetseveral requirements that often are in conflict. For example, therequirements associated with spinal stability and system reliabilityover an extended period of use often conflict with the requirements ofan easy to use implant. Strength requirements for a fusion plate tend tomake the plate bulky and adversely effect intra-operative andpostoperative viewing of the associate area of the spine. Additionally,it is desirable that the affected region of the cervical spine be easilyviewed using MRI or x-ray procedures to verify that the desired fusionof the cervical spine is complete and/or that the alignment of thecervical vertebrae is proper.

Plating systems are also required to ensure that bone screws do notloosen over time or back out from the plate, further complicating thedesign of anterior plating systems. It is further desirable to ensurethat the bone screws placed into the vertebrae through the platingsystem do not loosen or back out from the plate without requiringadditional surgical steps. Furthermore, locking mechanisms shouldadequately permit the removal of an associated bone screw when required,and allow sufficient angular freedom for bone screws relative to aplate.

It remains desirable in the pertinent art to provide an improvedanterior cervical plating system that addresses all the requirementsdiscussed above.

SUMMARY

The present teaching provide a bone fixation apparatus that includes abone fixation plate having a fixation hole, and a modular bone fixationfastener received in the fixation hole. The bone fixation fastenerincludes a shaft member and an expandable head member. The shaft memberhas an outer cam that mates with a corresponding inner cam of the headmember, such that upon rotation of the head member relative to the shaftmember, the head member radially expands to prevent back out of theshaft member relative to the bone fixation plate.

The present teachings also provide a bone fixation apparatus thatincludes a bone fixation plate having a fixation hole, and a modularbone fixation fastener received in the fixation hole. The fixation holehas a first diameter in a plane generally parallel to an upper surfaceof the bone fixation plate. The fixation fastener includes a shaftmember defining a shaft axis and an expandable head member carried bythe shaft member. The expandable head member is rotatable about theshaft axis relative to the shaft member between a first position and asecond position. In the first position the expandable head member has amaximum diameter that is smaller than the first diameter of the fixationhole, and in the second position the expandable head member has amaximum diameter that is greater than the first diameter.

The present teachings provide a bone fixation apparatus that includes abone fixation plate having a fixation hole, and a modular bone fixationfastener received in the fixation hole. The bone fixation fastenerincludes a shaft member having a head-receiving first end with amulti-radius outer surface defining a cam lobe, and an expandable headhaving a multi-radius inner surface defining a cam lobe mating with theshaft cam lobe, such that upon rotation of the head member relative tothe shaft member, the shaft cam lobe rotates out of alignment relativeto the head cam lobe forcing the head member to expand radially toprevent back out of the shaft member relative to the bone fixationplate.

The present teachings also provide a method for fastening bone portionsto each other. The method includes aligning a fixation plate forattachment to the bone portions, aligning a first cam defined in a firstportion of a modular fastener relative to a second mating cam defined ina second portion of the fastener, and inserting the modular fastener toone of the bone portions through a corresponding hole in the plate. Themethod further includes radially expanding a portion of the fasteneragainst the hole, to prevent back out of the fastener.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is an exploded view of a fixation apparatus according to thepresent teachings;

FIG. 2 a is an isometric view of a fixation plate for connecting twobone portions according to the present teachings;

FIG. 2 b is a top view of a fixation plate for connecting three boneportions according to the present teachings;

FIG. 2 c is a top view of a fixation plate for connecting four boneportions according to the present teachings;

FIG. 2 d is a top view of a fixation plate for connecting five boneportions according to the present teachings;

FIG. 3 is sectional view of a head member according to the presentteachings;

FIG. 4 is an isometric view of a head member according to the presentteachings;

FIG. 5 is top view of a head member according to the present teachings;

FIG. 6 is an isometric view of a shaft member according to the presentteachings;

FIG. 7 is an isometric view of another shaft member according to thepresent teachings;

FIG. 8 is a side view of the shaft member of FIG. 6;

FIG. 9 is a side view of the shaft member of FIG. 7;

FIG. 10 is a longitudinal sectional view of the shaft member of FIG. 8taken along line 10-10;

FIG. 11 is a longitudinal sectional view of the shaft member of FIG. 9taken along line 11-11;

FIG. 12 is an enlarged view of Detail D of FIGS. 8 and 9;

FIG. 13 is a sectional view of the Detail D of FIG. 12 along the axis13-13;

FIG. 14 is a top view of a bone fixation fastener according to thepresent teachings;

FIG. 15 is a sectional view of the bone fixation fastener of FIG. 14along axis 15-15;

FIG. 16 is sectional view of a detail of a bone fixation apparatusaccording to the present teachings;

FIG. 17 is an environmental view of a bone fixation system according tothe present teachings shown with a tool for inserting and removing thebone fixation fasteners;

FIG. 18 is an enlarged view of the tool shown in FIG. 17; and

FIG. 19 is a plan view of the tip of the tool shown in FIG. 18.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The following description of various embodiments is merely exemplary innature and is in no way intended to limit the invention, itsapplication, or uses.

FIG. 1 illustrates an exploded view of a bone fixation apparatus 100according to the present teachings. The bone fixation apparatus 100generally includes a bone fixation plate 102 and a modular bone fixationfastener 104. The bone fixation fastener 104 includes an expandable headmember 106 and a shaft member 108 having a shaft axis “C”. The bonefixation plate 102 includes one or more fixation holes 110 through whichthe bone fixation fastener 104 is inserted to be affixed to a boneportion.

FIGS. 2 a to 2 d illustrate examples of fixation plates 102 adapted forfixing together two to five bone portions 90, respectively, such as, forexample, the vertebral bodies shown in FIG. 16. In the exemplaryfixation plates 102 of FIGS. 2 a-2 d, the fixation holes 110 arearranged in pairs, two for each bone portion 90. Other arrangements arealso within the scope of the present teachings. For example, onefixation hole 110 for each bone portion 90 may be provided, or more thantwo fixation holes 110 for each bone portion 90 may be provided. Eachfixation hole 110 defines an inner surface 111, which may be spherical.

The fixation plate 102 can be shaped to conform to the bone portions 90and have a curvature in one or two directions defined by a longitudinalaxis “A” and a transverse axis “B”, as shown in FIG. 1. It will beappreciated that the axes A and B, shown as orthogonal in FIG. 1, neednot be so limited. Additionally, the fixation plate 102 can havedifferent shapes and it can also be planar.

The fixation plate 102 can include a viewing window 114 to help monitorthe location of any graft used in the fixation procedure and theprogress of fusion in post-operative X-rays and MRI scans of the boneportions 90. The viewing window 114 can be defined between the sets offixation holes 110 corresponding to contiguous bone portions orvertebral bodies 90, as shown in FIGS. 2 a-2 d. Additionally, thefixation plate 102 can include one or more anchoring holes 116 forpre-fixation anchoring or alignment using standard fasteners, such astacks or screws or just the shaft member 108 of the fixation fastener104.

Referring to FIGS. 3-5, the expandable head member 106 is bounded by anopen curved surface 118 defining a gap 120 and a central opening 122.The central opening 122 has an inner surface 124, and is adapted toreceive the shaft member 108. The gap 120 increases the resiliency ofthe head member 106, such that head member 106 can expand from a relaxedposition in which no pressure is exerted to the inner surface 124, to apressurized position in which pressure is exerted on the inner surface124 causing the gap 120 to widen. The inner surface 124 of the headmember 106 defines an inner head cam 126 with one or more lobes 128.Each lobe 128 of the inner head cam 126 can be constructed, for example,by offsetting a radius of a segment of the inner surface 124 by acertain radial distance and then connecting the offset regions withvariable radius curves.

FIGS. 6-13 illustrate shaft members 108 according to the presentteachings. In particular, FIGS. 7, 9 and 11 depict views of aself-drilling shaft member 108, while FIGS. 6, 8 and 10 depict views ofa self-tapping shaft member 108. The shaft member 108 includes aninsertion portion 130 having threads respectively adapted forself-drilling or self-tapping, and a distal portion 132 adapted to beretained by the head member 106. A magnified view of the distal portion132 is illustrated as Detail D in FIG. 12. A sectional view of thedistal portion 132 is shown in FIG. 13. The distal portion 132 defines aouter shaft cam 134 that has one or more lobes 136 adapted to mate withthe lobes 128 of the inner head cam 126 while the head member 106 is inthe relaxed position. In the relaxed position, the fixation fastener 104can rotate freely and be seated in the fixation plate 102 at variousangles relative to the plate 102.

When the head member 106 seats in the fixation hole 110 in the relaxedor unexpanded position, no pressure is exerted by the head member 106 tothe inner surface 111 of the hole 110. The curved surface 118 of thehead member 106 mates with the inner surface 111 of the fixation hole110, such that the head member 106 can rotate freely relative to theinner surface 111 of the fixation hole 110 in the relaxed position. Inthe pressurized or expanded position, the expanded head member 106 isexpanded toward the inner surface 111 of the hole 110.

Referring to FIG. 16, the head member 106 has a maximum diameter “D”which, in the unexpanded position of the head member 106, is smallerthan an upper diameter “d” of the fixation hole 110 of the fixationplate, such that the head member 106 can be inserted through thefixation hole 110. The upper diameter d of the fixation hole is definedin a plane 163 generally parallel to an upper surface 161 of thefixation plate. In the expanded position, the maximum diameter D isbigger than the upper diameter d of the fixation hole 110, preventingthe head member 106 from backing out of the fixation hole 110 at theupper surface of the fixation plate.

In one application, the expanded diameter of the head member 106 issufficiently large to press against the fixation hole 110. In thisparticular application, the expanded head member 106 not only preventsthe head member 106 from backing out of the fixation hole 110, but alsoarrests relative movement of the plate 102 and the fastener 108. Thisrelationship is referred to as a “constrained relationship”.

In another application, the expanded diameter of the head member 106remains sufficiently large to prevent the head member 106 from backingout of the fixation hole, but is not so large to preclude movementbetween the fastener 108 and the plate 102. In this regard, the headmember 106 is permitted to articulate relative to the fixation hole 110and thereby the fastener 108 may articulate relative to the plate 102.This relationship is referred to as a “semi-constrained relationship”.

In certain applications, the head member 106 and fastener 108 may becooperatively configured to alternatively provide both a constrainedmode of operation and a semi-constrained mode of operation. In thisregard, the lobes 128 of the head member 106 may cooperate with thelobes 136 of the fastener 108 to provide dual modes of operation.Explaining further, the head member 106 may be rotated from a relaxed orunexpanded state through a first rotation relative to the fastener 108to expand the head member 106 to a first expanded diameter and furtherrotated through a second rotation relative to the fastener 108 to expandthe head member 106 to a larger second expanded diameter. Similarly, thehead member 106 may be rotated in a first direction relative to thefastener (e.g., clockwise or counterclockwise) to expand the head member106 to the smaller first expanded diameter and further rotated in anopposite second direction to expand the head member 106 to the largersecond expanded diameter.

In operation, the fixation plate 102 may be temporarily attached to thebone portions 90 with shaft members 108 or other fasteners through theanchoring holes 116. Each fixation fastener 104 is assembled by aligningthe head member 106 with the shaft member 108 and placing the headmember 106 over the shaft member 108. Each fixation fastener 104 seatson a countersunk portion 138 of the fixation hole 110 such that it canfreely rotate, allowing the shaft member 108 to be placed in a desiredorientation and be drilled or tapped into the bone portion 90. Once theshaft member 108 is anchored in the bone portion 90, the head member 106can be rotated relative to the shaft member 108, such that the innerhead cam 126 rotates out of alignment relative to the outer shaft cam134 of the shaft member 108, causing the head member 106 to expand,thereby locking the fixation fastener 104 to the fixation plate 102 withcompression forces therebetween.

Referring to FIGS. 14, and 17-19, the head member 106 can include slotsor other engagement formations 140 for engaging the head member 106 witha first driver 158 to rotate the head cam 126 past the shaft cam 134 andcause the head member 106 to expand against the fixation hole 110,thereby locking the fixation fastener 104. The same driver 158 can beused to rotate the head member 106 in the opposite direction bringingthe head and shaft cams 126 and 134 in lobe alignment to unlock thefixation fastener 104. The shaft member 108 can also have internalthreads or other engagement formations 155 defined in an aperture 153 ofthe distal end 132, such that the shaft member 108 can be fastened toand unfastened from the bone 90 with a second driver 156 that hasexternal threads 160 shaped to be inserted in the aperture 153 andengage the internal threads 155.

Referring to FIGS. 18 and 19, the first and second drivers 158 and 156can be separate tools or can be combined in one tool 150 as follows. Thefirst driver 158 is attached to a torque handle 154, and is hollowdefining a bore 164. The second driver 156 is attached to a secondhandle 152 and passes through the bore 164. To insert the fixationfastener 104, the second driver 156 engages the internal threads 155 ofthe aperture 153 of the shaft member 108. The second handle 152 isrotated clockwise until the fixation fastener 104 is completely insertedinto the bone portion 90 and the head member 106 is level with thefixation plate 102. The torque handle 154 is then rotated clockwisewhile the first driver 158 engages the slots 140 of the head member 106,causing the head member 106 to expand and lock the fixation fastener104. To remove the fixation fastener 104, the reverse procedure isfollowed. The fixation fastener 104 is first unlocked by rotating thetorque handle 154 counterclockwise to re-align the head cam 126 with theshaft cam 134 and return the head member to its unexpanded state,thereby loosening the fixation fastener 104 from the fixation plate 102.The second handle 152 is then rotated counterclockwise to remove theshaft member 108 from the bone 90.

It will be appreciated that the fixation apparatus 100 provides quickfixation and/or removal of the plate 102 to the bone portions 90 forbone repairs, while preventing the fastener 104 from backing out of thebone portions 90 after fixation. Furthermore, the fastener 104 can bereadily oriented in a plurality of angles relative to the plate 102.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A bone fixation apparatus comprising: a bone fixation plate having afixation hole; a fastener shaft received in the fixation hole andincluding a first portion having an outer surface defining a first camand a second bone-engaging portion; and an annular member received inthe fixation hole and including an inner surface defining a second camfor cooperating with the first cam to selectively move the annularmember in a radial direction between an unexpanded position permittingmovement of the fastener shaft and annular member relative to thefixation hole and an expanded position restricting movement of thefastener shaft and annular member relative to the fixation hole, theannular member including at least one engagement formation operable toreceive a tool to move the annular member between the expanded positionand the unexpanded position by rotation of the annular member relativeto the fastener shaft following insertion of the fastener shaft into abone.
 2. The bone fixation apparatus of claim 1, wherein the first andsecond cams are configured to provide a semi-constrained mode ofoperation in which the fastener shaft is retained relative to the plateand the annular member is free to move within the fixation hole.
 3. Thebone fixation apparatus of claim 1, wherein the annular member has acurved outer surface mating with an inner surface of the fixation hole.4. The bone fixation apparatus of claim 3, wherein the outer surface ofthe annular member and an inner surface of the fixation hole arespherical.
 5. The bone fixation apparatus of claim 1, wherein theannular member has an expanded diameter sufficiently large to pressagainst the fixation hole and arrest relative movement between thefixation hole and the fastener shaft in the expanded position.
 6. Thebone fixation apparatus of claim 1, wherein the expanded positionincludes a first expanded position permitting movement of the fastenershaft and annular member relative to the fixation hole and a secondexpanded position preventing movement of the fastener shaft and annularmember relative to the fixation hole.
 7. The bone fixation apparatus ofclaim 1, wherein each of the first and second cams include threecontinuously curved lobes.
 8. The bone fixation apparatus of claim 1,wherein the fixation plate is a spinal fixation plate for securing firstand second vertebral bodies relative to one another.
 9. The bonefixation apparatus of claim 1, wherein the fastener shaft defines acircumferentially extending groove having a reduced diameter and theannular member is carried by the fastener shaft in the circumferentiallyextending groove.
 10. The bone fixation apparatus of claim 1, whereinthe annular member is coupled to the fastener shaft for relativearticulation therewith.
 11. The bone fixation apparatus of claim 1,wherein movement of the annular member between the expanded position andthe unexpanded position is independent from longitudinal translation ofthe fastener shaft relative to the annular member.
 12. A bone fixationapparatus comprising: a bone fixation plate having a fixation hole; afastener shaft having a bone-anchoring portion and an upper portiondefining an outer cam; and an annular member having an outer surface, aninner surface defining an inner cam, and at least one engagementformation, the at least one engagement formation operable to receive atool to rotate the annular member and cause the inner cam to cooperatewith the outer cam of the fastener shaft to move the annular memberbetween an unexpanded position and an expanded position independent frommovement of the fastener shaft relative to the bone fixation plate. 13.The bone fixation apparatus of claim 12, wherein the inner cam and theouter cam are configured to provide a semi-constrained mode of operationin which the fastener shaft is retained relative to the plate and theannular member is free to move within the fixation hole.
 14. The bonefixation apparatus of claim 12, wherein the annular member has anexpanded diameter sufficiently large to press against the fixation holeand arrest relative movement between the fixation hole and the fastenershaft in the expanded position.
 15. The bone fixation apparatus of claim12, wherein the expanded position includes a first expanded positionpermitting movement of the fastener shaft and annular member relative tothe fixation hole and a second expanded position preventing movement ofthe fastener shaft and annular member relative to the fixation hole. 16.The bone fixation apparatus of claim 12, wherein the fixation plate is aspinal fixation plate for securing first and second vertebral bodiesrelative to one another.
 17. The bone fixation apparatus of claim 12,wherein the fastener shaft defines a circumferentially extending groovehaving a reduced diameter and the annular member is carried by thefastener shaft in the groove such that the annular member is coupled tothe fastener shaft for relative articulation therewith.
 18. The bonefixation apparatus of claim 11, wherein the annular member isselectively moved between the expanded position and the unexpandedposition by rotation of the annular member relative to the fastenershaft.
 19. A bone fixation apparatus comprising: a bone fixation platehaving a fixation hole; a fastener shaft having a longitudinal axisextending between a first end and a second end thereof; acircumferential groove formed in the fastener shaft and having at leastone cam surface; and an annular member carried in the groove of thefastener shaft for relative articulation with the fastener shaft, theannular member having at least one engagement formation and defining anouter surface received within the fixation hole to allow orientation ofthe fastener shaft at various angles relative to the bone fixationplate, the annular member having an inner surface cooperating with theat least one cam surface of the fastener shaft to radially expand theannular member from an unexpanded position to an expanded position whena force is applied to the annular member at the at least one engagementformation to restrict the fastener shaft from backing out of thefixation hole.
 20. The bone fixation apparatus of claim 19, wherein theinner surface of the annular member and the outer surface of thefastener shaft are cooperatively configured to provide asemi-constrained mode of operation in which the fastener shaft isretained relative to the plate and the annular member is free to movewithin the fixation hole and a constrained mode of operation in whichthe fastener shaft is retained relative to the plate and the annularmember is fixed in the fixation hole.